Within the context of a continuing broad interest in leukocyte proliferation and differentiation, specific studies will attempt to: 1) Clarify the mechanisms involved in both the suppression and initiation of human lymphocyte proliferation in short term cultures; and 2) Further delineate the role of chromosome abnormalities in the disordered proliferation of leukocytes in vivo in human preleukemia and chronic leukemia. For the studies of lymphocyte suppression (1), a new feeder layer culture system will be used to assay human suppressor lymphocytes (and extracts) generated in mitogen stimulated bulk cultures, considering both their specific (immunological) and non-specific (chalone) effects. For the studies of lymphocyte "triggering", the cellular subpopulations and interactions involved in the mitogenic response to a calcium ionophore will be compared with the effects of lectin mitogens, and the findings correlated with a companion study of the early molecular events. For the chromosome studies (2), new banding techniques will be used to expand long-term studies concerned with the prognostic value of chromosomally-abnormal hemic cell clones in preleukemia, chronic granulocytic leukemia, and chronic lymphocytic leukemia, and the significance of these visible genetic changes in the evolution of human neoplastic cell populations.